Optical system for an infrared missile fuze

ABSTRACT

1. AN INFRARED FUZE COMPRISING AN ANNULAR TOROIDAL LENS, A PAIR OF ANNULAR DETECTORS POSITIONED CONCENTRICALLY WITH RESPECT TO THE AXIS OF SAID LENS AND ON OPPOSITE SIDES OF THE FOCAL POINT OF SAID LENS, SHIELDING AN REFLECTING MEANS ASSOCIATED WITH ONE OF SAID DETECTORS WHEREBY THE ENERGY PASSING THROUGH SAID LENS CROSSES THE AXIS THEREOF BEFORE STRIKING SAID DETECTOR, AND ELECTRONIC MEANS ASSOCIATED WITH SAID DETECTORS AND ADAPTED TO RECEIVE SUCCESSIVE SIGNALS FROM SAID DETECTORS DURING A PREDETERMINED INTERVAL FOR ACTUATING A DETONATION CIRCUIT.

NOV. 23, 1971 MUNDlE EI'AL 3,621,784

OPTICAL SYSTEM FOR AN INFRARED MISSILE FUZE Filed Dec. 29, 1955 2 Sheets-Sheet l PRE-AMP FILTER 5o SUMMING D TONATOR 49 AMPLIFIER E PRE- AMP Fl LTE R i INVENTOR.

LLOYD G. MUNDIE ATTORNE'YS NOV. 23, 1971 M DIE EI'AL 3,621,784

OPTICAL SYSTEM FOR AN INFRARED MISSILE FU'LE Filed Dec. 29, 1955 2 Sheets-Sheet 2 INVENTOR.

LLOYD G. MUNDIE 9 %100& ATTORz iw United States Patent U.S. Cl. 10270.2 P 9 Claims The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to a fuze and more particularly to an optical system for an infrared fuze adapted to be mounted in the nose of a missile which carries an explosive charge and detonate the explosive charge when the line of the sight from the missile to the target aircraft is inclined at a predetermined angle to the forward axis of the missile.

One prior method of detonating the explosive charge in the missile is radio fuzing in which reflection of radio waves initiates detonation. This method has low resolution because of the relatively long wavelengths used, and this leads to errors in timing the detonation and makes the device easy to jam. Another method is photoelectric fuzing in which visible radiation from the target actuates the fuze, but this method is inoperative at night and is subject to actuation by the sun and clouds. A third method utilizes infrared fuzing with the sector optical system, but, while this method is operative, both during the day and night, and is insensitive to the sun and clouds, it is complicated in that it requires six mirrors and six detectors. Furthermore, it is not uniform in sensitivity with the respect to azimuth.

The present invention in one preferred embodiment consists essentially of a toroidal-shaped lens which is cylindrically symmetrical about the missile axis and preferably ground on a curvature so that all portions thereof are focused at a point on the missile axis. A pair of annular detectors are mounted concentrically with respect to the missile axis with one above and one below the focal point of the toroidal lens. When the line of sight to the target is inclined at an initial angle to the central axis, such as 30 degrees, the radiation is brought to focus on the lower detector at this angle and the lower detector is activated to cause a momentary electrical signal pulse by the infrared radiation emanating from, reflected by, or interrupted by the target aircraft. At a later time the radiation is focused on the upper detector causing a secondary signal pulse. The first signal pulse is amplified, filtered, and applied to a summing amplifier. The second pulse from the upper detector is also amplified, filtered, and applied to the same summing amplifier. If the second voltage pulse occurs within a predetermined interval the sum of the two voltages is sufficient to actuate the detonator for the explosive charge. The filter passes only frequencies greater than 70 c.p.s. in order to discriminate against disturbing optical signals caused by yawing of the missile and passage through clouds, smoke puffs, etc., and the device is relatively immune to sunfiring because the sun never passes rapidly from the 30 to 60 position.

One object of the present invention is to provide a fuze which will detonate the explosive charge of a missile when the line of sight from the missile to the target aircraft is inclined at a predetermined angle to the forward axis of the missile.

Another object of the present invention is to provide an infrared fuze which is relatively simple to construct with a minimum of parts, and is uniform in sensitivity with respect to azimuth.

Another object of the present invention is to provide 3,621,784 Patented Nov. 23, 1971 a fuze which is accurate in timing the detonation and is not easy to jam.

A still further object of the present invention is to provide a fuze which is operative both day and night and is not subject to actuation by the sun and clouds, or other disturbing optical influences.

Still another object of the present invention is to provide a simple fuze which requires a small number of components which are inexpensive and easy to make, and wherein the parts are readily assembled, since the optical components are symmetrical and the two detectors are identical and consequently interchangeable.

Still another object of the present invention is to pro vide an optical system for an infrared fuze which can be adapted to a smaller missile or rocket than the more complex prior systems.

A still further object of the present invention is to provide an infrared fuzing system which is extremely simple electronically and one which can be readily miniaturized and has a very low overall power requirement.

A still further object of the present invention is to provide an optical system for an infrared fuzing system wherein the angle for actuating the detectors can be readily changed.

A still further object of the present invention is to provide an optical system for an infrared fuze which may be utilized either on the nose of the missile or in the waist, by proper choice of size and suitable design.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 is a pictorial view of one preferred embodiment of the present invention with a suitable mounting for testing of the device;

FIG. 2 is a sectional view taken along the center line of FIG. 1; and

FIG. 3 is a schematic block diagram illustrating one preferred manner of operating the fuze with the optical system of FIGS. 1 and 2.

Referring now to the drawings in detail, the fuze shown in FIGS. 1 and 2 consists of elements which are cylindrically svmmetrical about the missile axis.

The major part of the focussing is accomplished by means of the fuzed quartz lens 11 shown in FIGS. 1 and 2. The surfaces of this lens are generated by rotating the segment of a circle about the fuze axis. The base of the segment is preferably inclined at an angle of 45 degrees to the axis and the height of the segment is preferably equal to /2 of the diameter of the circle.

The radius at which the segment is rotated is chosen in such a way that parallel light entering the lens 11 in a direction perpendicular to the base of the segment is brought to a focus on the fuze axis at the point 12. It will be apparent that a detector located at this point will produce a system sensiive at a viewing angle of 45 degrees. For the reasons mentioned above, however, two viewing angles are desired; this is accomplished by mounting the two annular detectors 13 and 14 above and below the focal point 12. In this way radiation passing through the lens in a direction 15 degrees 01f axis on either side of center is utilized, resulting in the preferred viewing angles of 30 and 60.

In order to avoid having a portion of the desired radiation miss the upper detector completely, the annular mirror or conical reflector 15 is mounted above the surface of the detector 13. The paths followed by the radiation entering the system are indicated by the light lines 16 and 17 with the rays 16 at an angle of 30 to the axis being focused by the lens 11 on the lower detector 14 and rays 17 at an angle of 60 being reflected from the conical reflector 15 and striking the upper detector 13 directly. In order to minimize the effect of background radiation baflles 18, 19 and 21 are provided. Baffle 21 also serves the function of a spacer, as described infra.

If desired, appropriate optical filters may be located adjacent to the inner surface of the lens 11 as indicated by the numeral 22, or such filters may be applied to the lens as a coating thereon.

The block 23 is provided with a conical flange 24 which restricts the aperture of the lens 11, together with the conical portion of the cylindrical supporting member 25. The aperture may be further restricted by opaque paint on the outer curved surface of the lens as indicated by the numerals 26 and 27 in FIGS. 1 and 2.

The block 28 is secured to the block 273 by suitable means such as the machine screw 29, and in actual practice on the nose of a missible block 28 would be a suitably shaped nose piece. For test purposes the entire assembly is shown as mounted on a base 31, which is provided with a recess 32 adapted to contain the electronic components for use with the optical system and detectors 13 and 14. In actual practice the base 31 would probably be replaced by another part of the missile or a section adapted to be secured to the next adjacent section of the missile.

The lens 11 is preferably attached to the supports 23 and 25 by the use of a suitable cement. However, should greater mechanical strength be required, a suitable structure for mechanically retaining the lens 11 in a fixed position and a set of radial supporting vanes could be utilized.

The set screws 33 and 34 serve to fix the position of the sleeve 25 with respect to the base 31, and by this means the lens 11 may be focused with respect to the detectors 13 and 14 for activation at the desired angles, or the specific viewing angles may be changed by altering the position of the annular lens along the fuze axis and/or by changing the length of the spacer 21 that separates the two detectors 13 and 14.

While the lens 11 has been indicated supra as being made of fuzed quartz. it will be apparent that the lens material could be changed to any other glassy or crystalline optical material which would transmit wave lengths ranging from 2,000 A. to 15 microns, such as glass, arsenic trisulfide, thallium bromide iodide, arsenic telluride sulfide, arsenic trisellenide, arsenic tritelluride, Vycor, or silver chloride.

The two annular detectors 13 and 1 4 are preferably formed of lead sulfide deposited on a reflecting surface to improve their sensitivity but may be formed of any photosensitive intermetallic compound capable of detecting radiation at Wavelengths from 2,000 A. to 15 microns and which can be formed into an annular shape, such as cadmium sulfide, cadmium selenide, lead telluride, germanium, and doped germanium.

The aperture of the lens 11 can be increased by contacting the annular detector to the annular lens after the principle of the immersion microscope. The annular detector may also be evaporated or chemically deposited on the inner surface of the primary lens in which case two lenses would be needed to achieve the two viewing angles.

The device may also be used with hermetic sealing so that it may be evacuated or filled with any gas so as to improve its reliability, sensitivity, or time constant.

Nonreflecting coatings or interference filters may be applied to any of the optical components to improve the operating characteristics of the fuze or to adapt it to any particular usage.

The schematic block diagram of FIG. 3 illustrates one preferred manner of operating the fuze illustrated in FIGS. 1 and 2 wherein the two annular detectors 13 and 14 are provided with electrodes 41, 42, 43, and 44. The electrodes 42 and 44 are connected to ground and the electrodes 41 and 43 are connected to the preamplifiers 45 and 46. The amplified signals from the preamplifiers 45 and 46 are filtered through the filters 47 and 48 which may be built into the preamplifiers 45 and 46. These filters 47 and 48 are high pass filters which will only pass frequencies greater than c.p.s. in order to discriminate against disturbing optical signals caused by yawing of the missile and its passage through clouds, smoke puffs, and other disturbing influences. The signals from the detectors 13 and 14 passing through the preamplifiers 4 5 and 46 and through the filters 47 and 48, both go to the summing amplifier 49 which actuates the detonator 50 when--- t he two voltages occur within a predetermined period of time.

OPERATION 111 operation of the device on a missile in flight it is actuated by the infrared radiation emanating from, reflected by, or interrupted by the target aircraft. When the line of sight to the target is inclined at an angle of 30 to the missile axis the rays 16 are brought to focus on the annular detector 14, and passage of the aircraft image across the detector 14 causes a momentary electrical signal pulse which is amplified by the preamplifier 46, filtered by the .filter 48 and applied to the summing amplifier 49. When the line of sight increases from 30 to 60 as a consequence of the forward motion of the missile, the rays 17 arising from the target in its new position are focused on the detector 13 by the lens 11 with the aid of the annular mirror or reflector '15. The passage of the image of the target across the upper detector 13 produces a second electrical pulse which is likewise amplified by the amplifier 45, filtered by the filter 47 and applied to the summing amplifier 49. If the second voltage pulse arrives at the summing amplifier 49 within a predetermined time after the first signal pulse from the detector 14, the sum of the two voltages will be suflicient to provide an output from the summing amplifier 49 to actuate the detonator 50.

An alternative method (not shown) of actuating the detonator from the detectors 13 and 14 would be to amplify and filter the signals from each of the detectors and apply them to the same condenser, so that the second pulse adds to what remains of the first pulse. If the second voltage pulse arrives at the condenser before the first pulse has leaked off, the sum of the two voltages would be suflicient to fire a thyratron whose grid is also connected to the condenser. Detonation of the explosive charge would then be caused by the firing of this thyratron.

While two separate detectors have been shown in the preferred embodiment, it may be feasible to provide suitable baflies and reflectors to focus both bundles of rays 16 and -17 on a single detector in succession to provide two spaced pulses for summing and actuation of the detonator.

It will be apparent that the band pass of the filters 47 and 48 can be modified according to the intended application in order to achieve improved discrimination against optical background signals or to provide operation of the fuze in the manner desired.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. An infrared fuze comprising an annular toroidal lens, a pair of annular detectors positioned concentrically with respect to the axis of said lens and on opposite sides of the focal point of said lens, shielding and reflecting means associated with one of said detectors whereby the energy passing through said lens crosses the axis thereof before striking said detector, and electronic means associated with said detectors and adapted to receive successive signals from said detectors during a predetermined interval for actuating a detonation circuit.

2. An infrared fuze comprising an annular toroidal lens, a pair of annular detectors positioned concentrically with respect to the axis of said lens and on opposite sides of the focal point of said lens, shielding and reflecting means associated with one of said detectors whereby the energy passing through said lens crosses the axis thereof before striking said detector, and electronic means associated with said detectors and adapted to receive successive signals from said detectors above a predetermined frequency and occurring during a predetermined interval for actuating a detonation circuit.

3. An infrared fuze comprising an annular toroidal lens, a pair of annular detectors positioned concentrically with respect to the axis of said lens and on opposite sides of the focal point thereof, means including a preamplifier and filter associated with each of said detectors for passing signals above a predetermined frequency received from said detectors, and means including a summing amplifier associated with both filters for adding said signals occurring within a predetermined interval for actuating a detonation circuit.

4. An infrared fuze comprising an annular toroidal lens, a pair of annular detectors positioned concentrically with respect to the axis of said lens and on opposite sides of the focal point thereof, means for focussing energy incident at two different angles on separate ones of said detectors, means including a preamplifier and filter associated with each of said detectors for passing signals above a predetermined frequency received from said detectors, and means including a summing amplifier associated with both filters for adding said signals occurring within a predetermined interval for actuating a detonation circuit.

5. An optical system for a fuze comprising an annular lens of toroidal shape, said lens being adapted to focus at a point adjacent the axis thereof, a pair of annular detectors concentric with the axis of said lens, one of said detectors being positioned above said focal point and the other detector being positioned below said focal point, and means for directing incident energy passing through said lens at each of two different angles to one of said detectors.

6. An optical system for a fuze comprising an annular lens of toroidal shape, said lens being adapted to focus at a point adjacent the axis thereof, a pair of annular detectors concentric with said axis, one of said detectors being positioned above said focal point and the other detector being positioned below said focal point, and a reflector for reflecting incident energy onto said upper detector and shielding said detector so that energy passing through said lens crosses the axis thereof before striking said upper detector.

7. An infrared fuze system for a missile comprising an annular lens mounted concentrically with the longitudinal axis of said missile whereby the focal point of said lens lies on said axis, a pair of annular infrared photoconductive detectors mounted concentrically with said axis and spaced apart axially on either side of said focal point whereby energy passing through said lens at two different angles due to presence of a target generates a distinct signal from each detector.

8. The fuze system according to claim 7 further provided with a preamplifier and filter associated with each of said detectors for passing said signals from said detectors above a predetermined frequency and a summing amplifier for adding the passed signals occurring during a predetermined interval for actuating a detonation circuit.

9. The fuze system according to claim 7 further provided with a shielding and reflecting means associated with one of said detectors whereby the energy passing through said lens crosses the axis thereof before striking said detector.

References Cited UNITED STATES PATENTS 2,415,348 2/1947 Haigney 10270.2 P 2,699,834 1/1955 OBrien 88-1 Hws FOREIGN PATENTS 159,839 8/1953 Australia 10270.2 P 520,196 11/1953 Belgium lO2--70.2 P 585,792 2/1947 Great Britain. 731,849 2/ 1943 Germany.

BENJAMIN A. BORCHELT, Primary Examiner T. H. WEBB, Assistant Examiner 

